Bubbling and Local Blister of plywood in summer 2020

Bubbling and Local Blister of plywood in summer 2020

Bubbling refers to the bulge caused by the gas on the product surface. Partial local delamination means that some part of the plywood  is not bonded firmly and cracks. The bubbling and local delamination problems should be analyzed and controlled from the following aspects:

1) The moisture content of single core veneer is too high or uneven. The moisture content of veneer affects the quality of plywood to a great extent, too high and too low are not conducive to plywood production. Therefore, the moisture content of veneer after drying should be strictly controlled within the range of 8% – 14%. If the moisture content is too high, it is easy to delaminate and bubble.

2) When applying glue, there are some blank spots or sundries on the veneer or they are stuck. In order to ensure the quality of glue application, the amount of glue application shall be even, and the parts not applied to the glue shall be manually brushed, no blank points are allowed, and redundant glue shall be removed at the place where the glue is piled up. For the sundries and dirt on the veneer, it must be cleaned.

3) Unreasonable hot pressing process, such as insufficient hot pressing time, low local hot pressing temperature, resulting in insufficient resin condensation. In the whole plywood production process, the hot pressing process always needs to be strictly controlled, and the hot pressing process parameters that meet the production needs must be selected according to different products.

4) After hot pressing, the pressure reduction speed is too fast. In the plywood production process, the speed of decreasing from equilibrium pressure to zero should be well controlled. In this stage, the speed of reducing pressure should be slow, so that the temperature of hot pressing can be properly reduced, and the water vapor in the board can be discharged too fast, which is easy to generate bubbles.

In addition, in summer, due to the dry weather and extremely high temperature, the veneer core after laid up needs to be cold pressed and hot pressed in time to prevent the loss of glue activity and the degradation of glue performance.

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